[ANN] Rails 5.2.1.rc1 has been released!

[ANN] Rails 5.2.1.rc1 has been released!

Hi everyone,

I am happy to announce that Rails 5.2.1.rc1 has been released.

If no regressions are found, expect the final release on Monday, August 6, 2018.
If you find one, please open an [issue on GitHub](https://github.com/rails/rails/issues/new)
and mention me (@rafaelfranca) on it, so that we can fix it before the final release.

## CHANGES since 5.2.0

To view the changes for each gem, please read the changelogs on GitHub: